This invention relates to the cooling of flat semiconductor components such as disc-type thyristors in general, and more particularly to an improved cooling arrangement which permits cooling a plurality of such semiconductors arranged in a column-like cooling stack.
Arrangements for cooling disc-type thyristors and other flat semiconductors in which the semiconductor is clamped in good thermal contact between two cooling elements of thermally highly conductive material each having at least one heat pipe, with fins on its end attached transversely to the heat pipe axis, disposed in an elongated recess therein have been developed. Heat pipes have been found particularly useful in such an application. As is well known in the art, heat pipes comprise a pipe of thermally conductive material closed on both ends and lined on the inside with a wick. The heat pipe is partially filled with an evapoarable working fluid. An arrangement such as this is disclosed in Belgian Pat. No. 794,501.
The heat pipe can be inserted into the recess in the cooling element with an end of the heat pipe therein and the other end with fins protruding. An arrangement is also possible where the heat pipe extends through the recess, centered therein, with cooling fins pushed or placed on the heat pipe on both sides of the cooling element. The heat pipe is preferably soldered, shrunk or screwed into the recess for better thermal contact. As an example, the recess may be a hole which is formed parallel to the contact surface of the semiconductor component and the cooling element. Preferably, straight heat pipes are used.
In this prior art cooling arrangement, heat developed by the semiconductor component and given off by the cooling element is conducted to the cooling fins through the working fluid and to a small extent, also through the wall of the heat pipe and is removed from the cooling fins through the use of a cooling medium directed thereover by convection or by means of a blower. As compared to other known arrangements for cooling semiconductor components, this cooling arrangement requires less material for the two cooling elements which typically consist of copper or aluminum. As a result, it can be produced more readily and inexpensively for a given cooling capacity.
In practice, e.g., in heavy duty drives or for high voltage dc transmission, flat semiconductor components such as disc thyristors are frequently connected in series or parallel to form a single valve or controlled rectifier. It is common in such an electrical arrangement to also arrange the individual semiconductor components physically close together and in particular, to stack them one over the other. For example, German Offenlegungsschrift No. 1,564,694 teaches combining a plurality of this type of semiconductor rectifiers in a column-like cooling stack with alternating cooling elements between the disc thyristors. In this arrangement, a cooling liquid flows through the individual cooling elements. A typical clamping device clamping together at least two such cooling stack arrangements is disclosed in German Auslegeschrift No. 1,614,640.
Clearly, this arrangement is more complex and costly than the heat pipe arrangement disclosed herein above. Thus, it is clear that there is a need for an improved cooling arrangement for stacked flat semiconductors which can: (1) take advantage of the benefits of the heat pipe; and (2) in addition, provide adequate cooling to the semiconductors no matter what their location is within the column or stack. That is, the problem is to provide an arrangement in which cooling air of essentially the same temperature can flow over all the heat pipes in such an arrangement.